1. Field of the Invention
The ability to employ naturally occurring receptors or antibodies directed to specific compounds in assaying for the presence of a compound of interest has created a burgeoning immunoassay business. In each of the assays, a complementary pair of specific binding pair ("sbp") members, usually an immunological pair, involving a ligand and a receptor (antiligand) is involved, wherein one of the sbp members is labeled with a label which provides a detectable signal. The immunoassay methodology results in a distribution of the signal label between signal label bound in a complex of the sbp members and unbound signal label. The differentiation between bound and unbound signal label can be as a result of physical separation of bound from unbound signal label or modulation of the detectible signal between bound and unbound signal label.
For the most part, immunoassays have been directed to quantitative determination of a wide variety of compounds of interest in clinical laboratories requiring relatively sophisticated equipment and careful technique. Immunoassays have found less extensive commercial application where semi-quantitative or qualitative results would be acceptable and the determination would involve non-laboratory personnel, such as in a home or a medical practitioner's office. Even in the clinical laboratory, simple and rapid screening tests employing inexperienced personnel could serve to provide substantial economies.
In developing an immunoassay, there are many considerations. One consideration is to provide substantial differentiation between the observed signal resulting from signal label when bound as compared to unbound. Another consideration is to minimize interference from endogenous materials in the sample suspected of containing the compound of interest. A further consideration is the ease with which the observed signal can be detected and serve to differentiate between concentrations in the concentration range of interest. Another consideration is the concentration of the compound of interest in a sample. Other factors include the ease of preparation of the reagents, the precision with which samples and reagent solutions must be prepared and measured, the storage stability of the reagents, the number of steps required in the protocol, and the proficiency and accuracy with which each of the steps must be performed. Therefore, in developing an assay that can have application with untrained personnel, such as assays to be performed in the home, in forensic medicine, by medical practitioners, or the like, the observed result should be minimally affected by variations in the manner in which the protocol is carried out and the techniques for performing the various steps should be simple.
In general, immunoassays that permit the determination of a dilute analyte in a sample have been difficult to design and those that have been demonstrated require numerous steps and long periods of time.
Frontal analysis (or breakthrough analysis) is a known method for quantitating active groups on a solid support in a chromatography column (C. R. Lowe and P. D. G. Dean, Affinity Chromatography, John Wiley & Sons, Ltd., New York, 1974). In frontal analysis, a solution of the reacting species at a known concentration is applied to the column. Measurement of the volume needed to saturate the column so that the reacting species is detected in the column effluent (the breakthrough volume) allows determination of the active group concentration on the column.
2. Description of the Related Art
U.S. Pat. No. 4,425,438 describes a method and device for assaying a test substance utilizing a primary absorbent substance for selectively allowing only a quantity of an analytical reagent proportional to the quantity of test substance to pass therethrough when test substance and analytical reagent are contacted with the primary absorbent. An analytical absorbent is disposed in a series of zones for sequentially absorbing the analytical reagent which passes through the primary absorbent so that detection of the last zone of absorbed analytical reagent indicates the quantity of test substance. In the method test substance and analytical reagent are passed through the primary absorbent and then the analytical absorbent followed by detection of the last zone in which analytical reagent is absorbed. The device is a funnel with the primary absorbent therein for directing the test substance and analytical reagent to a narrow tube holding the analytical absorbent.
A test device for determining a characteristic of a sample, particularly for determining substances in fluid samples, is disclosed in U.S. Pat. No. 4,094,647. A thin layer chromatography device and method of making a chromatography test is disclosed in U.S. Pat. No. 4,384,958. An immunoassay wherein labeled antibody is displaced from immobilized analyte analog is described in U.S. Pat. No. 4,434,236. A device and method for detecting myoglobin is disclosed in U.S. Pat. No. 4,189,304. Test strips for analyzing substances dissolved in liquids are described in U.S. Pat. No. 4,438,067. A multi-layered test device for determining the presence of a liquid sample component and the method of using such a device, are described in U.S. Pat. No. 4,160,008. A method for measuring antigen by labeled antigen using insoluble antibody is disclosed in Japanese Patent Application Laid-Open No. 5925/73--Jan. 25, 1973.
A concentrating zone method in heterogeneous immunoassays is disclosed in U.S. Pat. No. 4,366,241. U.S. Pat. No. 4,168,146 describes an immunoassay test strip. U.S. Pat. Nos. 3,990,850 and 4,055,394 describe diagnostic test cards. An automated method for quantitative analysis of biological fluids is described in U.S. Pat. No. 4,327,073. A chromogenic support immunoassay is disclosed in International Application No. PCT/US83/01887. A heterogeneous immunoassay for digoxin using ouabain as a separation means is described in U.S. Pat. No. 4,551,426.
A wide variety of patents and patent applications provide an extensive literature of different techniques for producing detectible signals in immunoassays. The following list is merely illustrative of some of these techniques which can find application in this invention. The following is a list of United States patents and patent applications and a general statement of the type of label involved:
U.S. Pat. Nos. 3,646,346, Radioactive Label; 3,654,090, 3,791,932 and 3,817,838, Enzyme Labels; 3,996,345, Fluorescer-Quencher Labels; 4,062,733, Radioactive Label; 4,067,959, Fluorescer or Enzyme Label; 4,104,029, Chemiluminescent Label; and 4,160,645, Non-Enzymatic Catalyst Label. See U.S. Pat. Nos. 3,966,879 for an electrophoretic technique employing an antibody zone and 4,120,945 for an RIA where labeled analyte is initially bound to a solid support through antibody. U.S. Pat. No. 4,233,402 employs enzyme pair labels; U.S. Pat. No. 4,720,450, chemically induced fluorescent labels; and U.S. Pat. No. 4,287,300, enzyme anionic charge labels.